WO2021194201A1 - Super absorbent polymer film and preparation method thereof - Google Patents

Abstract

The present invention relates to a super absorbent polymer film and a preparation method thereof. Specifically, the present invention relates to a new type of super absorbent polymer film which is thin with excellent absorption performance, flexibility, and retractility, can minimize changes in product shape, is unlikely to be scattered or leak , and does not need an auxiliary agent such as pulp, etc., thus enabling the product to be thin and reducing manufacturing processes and costs.

Description

Superabsorbent polymer film and manufacturing method thereof

Cross-Citation with Related Application(s)

This application claims the benefit of priority based on Korean Patent Application No. 10-2020-0035145 dated March 23, 2020 and Korean Patent Application No. 10-2021-0036937 dated March 22, 2021, All content disclosed in the literature is incorporated herein by reference.

The present invention relates to a superabsorbent polymer film and a method for manufacturing the same.

Super Absorbent Polymer (SAP) is a synthetic polymer material that can absorb water 500 to 1,000 times its own weight. Material), etc., are named differently. The superabsorbent polymer as described above started to be put to practical use as sanitary products, and now, in addition to sanitary products such as paper diapers and sanitary napkins for children, it is a soil repair agent for horticulture, water repellent material for civil engineering and construction, a sheet for seedlings, and a freshness maintenance agent in the food distribution field. , and is widely used as a material for poultice.

In general, sanitary products such as various diapers, sanitary napkins or incontinence pads include absorbents containing superabsorbent polymer particles. These absorbents are mainly superabsorbent polymer particles and the absorbent body and hygiene products while properly fixing the superabsorbent polymer particles. It was common to use fluff pulp to maintain its shape.

However, due to the existence of such fluff pulp, it was difficult to slim and thin the absorbent body and hygiene products, and there was a problem in that the fit was poor, such as sweating between the user's skin and the hygiene product. Moreover, since fluff pulp is mainly obtained from wood as a raw material, there is a point against the recent environmental protection trend, and the use of fluff pulp is also one of the main causes of increasing the manufacturing cost of sanitary products.

In addition, most of the current superabsorbent polymers are manufactured and used in the form of powder. These superabsorbent polymers in powder form may scatter or leak when manufacturing sanitary materials or in actual use, and have a specific type of substrate. Because it has to be used together with a substrate, there is a limit to the range of use and thinning. In addition, since the absorption performance of the absorber may change depending on the content distribution of the superabsorbent polymer particles, it is difficult to uniformly control the absorption characteristics.

On the other hand, in order to solve the above problems, a sheet-type super absorbent polymer has been proposed.

For example, a method for producing a sheet-type superabsorbent polymer by kneading an acrylic acid-based monomer or pulverizing a hydrogel polymer obtained after polymerization to obtain a particulate hydrogel polymer and then molding the polymer is known. However, since the diameter of the hydrogel polymer particles is about 0.2 to 2.0 mm, the method has a limitation in realizing an ultra-thin sheet having a thickness of 0.5 mm or less, and in order to secure shape retention and absorbency, such as fluff pulp There was a problem that supplements were still required.

Accordingly, there is a need for research on a new type of superabsorbent polymer that does not require an auxiliary agent such as fluff pulp, can be reduced in thickness, and exhibits excellent absorbent properties, and a method for manufacturing the same.

[Prior art literature]

Patent Document 1: Japanese Patent Application Laid-Open No. Hei 08-73507

Patent Document 2: Japanese Patent Application Laid-Open No. Hei 09-183856

In order to solve the above problems, the present invention provides a film-type superabsorbent polymer that can replace the existing powder-type superabsorbent polymer and a method for manufacturing the same.

According to one embodiment of the present invention, there is provided a superabsorbent polymer film comprising a polymer having an acidic group and polymerized with an acrylic acid-based monomer in which at least a portion of the acidic group is neutralized, the superabsorbent polymer film comprising:

having a thickness of 0.001 to 0.5 mm,

a centrifugal retention capacity (CRC) of 23 g/g or more, measured according to EDANA method WSP 241.2;

A superabsorbent polymer film having an elongation of 100% or more calculated by Equation 1 below is provided:

[Equation 1]

Elongation (%) = (L _1- L ₀ )/L ₀ *100

In Equation 1 above,

L ₀ is the initial gage distance,

L ₁ is the gage point distance at the time of fracture when the specimen is pulled at a rate of 0.5 mm per minute.

Preferably, the superabsorbent polymer film has a centrifugation retention capacity of 23 g/g to 50 g/g and an elongation of 100% to 550%.

Preferably, the superabsorbent polymer film is formed by immersing the superabsorbent polymer film cut into a circular shape in 0.9% by weight of an aqueous sodium chloride solution and swelling for 60 minutes. The anisotropy is 1.5 or more, or 1.5 to 5.

[Equation 2]

In Equation 2 above,

h is the initial thickness of the superabsorbent polymer film, h' is the thickness after swelling,

d is the initial diameter of the superabsorbent polymer film, and d' is the diameter after swelling.

Preferably, the superabsorbent polymer film has a total light transmittance of 89.5% or more.

According to another embodiment of the present invention, preparing a monomer composition by mixing an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized, a cellulose-based thickener, a moisturizing agent, a polymerization initiator, and a solvent; casting the monomer composition on a substrate to form a film of the monomer composition; forming a hydrogel polymer film by irradiating heat and/or light while stretching the monomer composition film; and drying the hydrogel polymer film is provided.

The cellulose-based thickener may be at least one selected from the group consisting of nanocellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and sodium carboxymethylcellulose.

The moisturizer is glycerin; diglycerin; ethylene glycol; propylene glycol; butylene glycol; sorbitol; polyethylene glycol; polyglycerin-3; polyglycerin-6; polyglycerin-10; an ester compound of polyglycerol-10 and a saturated fatty acid having 3 to 18 carbon atoms; citric acid; triethyl citrate; methyl citrate; sodium citrate; And it may be at least one selected from the group consisting of trisodium 2-methylcitrate.

The cellulose-based thickener may be included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the solid content in the monomer composition.

The moisturizing agent may be included in an amount of 5 to 70 parts by weight based on 100 parts by weight of the acrylic acid-based monomer.

The viscosity at 25° C. of the monomer composition may be 100 mPa·s or more.

In the step of forming the hydrogel polymer film, the tension applied to the monomer composition film may be 40 to 100 N/m.

The superabsorbent polymer film of the present invention exhibits excellent absorption performance while being thin in thickness, has excellent flexibility and stretchability, and exhibits little change in product shape.

In addition, the superabsorbent polymer film of the present invention does not have to worry about scattering or leaking from the product during product manufacturing, and since an auxiliary agent such as fluff pulp is unnecessary, the product can be made thinner, and the manufacturing process and cost can be reduced.

The terminology used herein is used to describe exemplary embodiments only, and is not intended to limit the present invention. The singular expression includes the plural expression unless the context clearly dictates otherwise. In this specification, terms such as "comprises", "comprises" or "have" are intended to designate the presence of an embodied feature, step, element, or a combination thereof, but one or more other features or steps; It should be understood that the possibility of the presence or addition of components, or combinations thereof, is not precluded in advance.

Since the present invention may have various changes and may have various forms, specific embodiments will be illustrated and described in detail below. However, this is not intended to limit the present invention to the specific disclosed form, it should be understood to include all modifications, equivalents and substitutes included in the spirit and scope of the present invention.

Hereinafter, the present invention will be described in detail.

According to one embodiment of the present invention, a superabsorbent polymer film having an acidic group and comprising a polymer polymerized with an acrylic acid-based monomer in which at least a portion of the acidic group is neutralized, the superabsorbent polymer film having a thickness of 0.001 to 0.5 mm, according to EDANA method WSP 241.2 A superabsorbent polymer film having a measured centrifugal retention capacity (CRC) of 23 g/g or more and an elongation of 100% or more calculated by Equation 1 below is provided:

[Equation 1]

Elongation (%) = (L _1- L ₀ )/L ₀ *100

In Equation 1 above,

L ₀ is the initial gage distance,

L ₁ is the gage point distance at the time of fracture when the specimen is pulled at a rate of 0.5 mm per minute.

In general, the superabsorbent polymer is obtained by polymerizing an acrylic acid-based monomer in the presence of an internal crosslinking agent to obtain a hydrogel polymer, drying, pulverizing and classifying it to prepare a base resin, and then performing surface modification. The superabsorbent polymer prepared in this way is in the form of a powder having a particle size in the range of about 200 to 600 μm, and is mixed with an auxiliary agent such as fluff pulp and then compounded and then applied to the product.

However, powdered superabsorbent polymers have a risk of scattering or leaking from the product during the manufacturing process of the absorbent core, and it is difficult to uniformly control the absorption performance due to difficult dispersion in the product. there was.

In addition, it is known that the conventionally developed sheet-type superabsorbent polymer is manufactured by rolling a powder or particulate superabsorbent polymer or fixing the superabsorbent polymer to a support such as a nonwoven fabric for shape retention. However, the sheet-type superabsorbent polymer produced by this method has low process efficiency due to a complicated manufacturing method, and requires many components other than the superabsorbent polymer to fix the support and the support, so that the content of the superabsorbent polymer present in the final product Absorption properties are not good because there is a limit to increase the In addition, even when a powder or particulate superabsorbent polymer or a particulate hydrogel polymer is rolled and molded into a sheet, the manufacturing method is complicated and the product is limited in thinning because it has to go through the mixing and molding process of the molding aid after polymerization of the monomer. In order to bind the superabsorbent polymer and form a sheet, molding auxiliary materials such as fibers or pulp must be included inevitably, so the absorption characteristics are also poor.

Accordingly, the present inventors have conducted research on a new type of superabsorbent polymer that does not require an auxiliary agent such as pulp, can be thinned, has no fear of scattering, and can be used as an absorber as it is, and as a result, the present invention has been reached.

The superabsorbent polymer film of the present invention has a thin film form rather than a powder, so there is no fear of scattering or leakage from the product during handling, and it can be used without a separate auxiliary agent such as fluff pulp, and exhibits excellent absorption properties by itself.

In the present invention, the term "super absorbent polymer film" refers to a superabsorbent polymer having a moisture content of 15% or less, or 12% or less, preferably 11% or less, and having a flexible, thin layer or membrane form. Preferably, the water content of the superabsorbent polymer film is 15 wt% or less, or 12 wt% or less, or 11 wt% or less, or 10 wt% or less, and 1 wt% or more, or 2 wt% or more, or 4 wt% % or more, or 6 wt% or more.

Meanwhile, throughout the present specification, "moisture content" indicates the amount of moisture contained in the sample as a percentage with respect to the weight of the sample before drying. That is, the moisture content can be calculated by dividing a value obtained by subtracting the weight after drying of the sample from the weight before drying of the sample by the weight before drying of the sample and then multiplying by 100. At this time, the drying condition is set to 20 minutes including 5 minutes of the temperature rise step in such a way that the temperature is raised from room temperature to about 150°C and then maintained at 150°C.

In one embodiment, the superabsorbent polymer film may have a moisture content of 15% or less, and may be in a transparent, elastic, and flexible film form.

When the superabsorbent polymer film is transparent, it means that the total light transmittance with respect to visible light is 89.5% or more when the thickness is in the range of 0.001 to 0.5 mm. The total light transmittance of the superabsorbent polymer film according to an embodiment of the present invention may be 90% or more, or 90.4% or more, or 91% or more, or 91.5% or more, or 92% or more. The total light transmittance may theoretically be 100%, for example, it may be 99% or less.

In addition, the superabsorbent polymer film of the present invention may have a yellowness index of 2.6 or less, 2.5 or less, 2.4 or less, 2.3 or less, 1.9 or less, 1.5 or less, or 1.3 or less according to ASTM D1925 standard in a thickness range of 0.001 to 0.5 mm. have.

The superabsorbent polymer film of the present invention has a thickness of 0.5 mm or less, preferably 0.4 mm or less, or 0.3 mm or less, or 0.2 mm or less, or 0.1 mm or less and 0.001 mm or more, or 0.005 mm or more, or 0.01 mm or more, Alternatively, it is possible to implement a thinner absorbent than the conventional powder-type super absorbent polymer with a thickness of 0.05 mm or more.

The superabsorbent polymer film of the present invention has a centrifugal retention capacity (CRC) of 23 g/g or more, 25 g/g or more, 28 g/g or more, 30 g/g or more, or 33 measured according to EDANA method WSP 241.2. It exhibits excellent absorption properties in g/g or more. A method for measuring the centrifugal water retention capacity of the superabsorbent polymer film may be embodied in Examples to be described later.

Centrifugation retention capacity is superior as the value is higher, and there is no theoretical upper limit, but may be, for example, 50 g/g or less, or 48 g/g or less.

In addition, the superabsorbent polymer film of the present invention exhibits excellent water holding capacity as described above and high elongation.

Specifically, the superabsorbent polymer film of the present invention has a thickness of 0.001 to 0.5 mm, an elongation of 100% or more, 120% or more, 150% or more, 180% or more, or 200% or more, and 550% or less, 530% or less , or 510% or less. In this case, the elongation may be calculated according to Equation 1, and the measurement method may be embodied according to an embodiment to be described later.

Preferably, the superabsorbent polymer film may have a centrifugal retention capacity of 23 g/g to 50 g/g and an elongation of 100% to 550%.

Preferably, the superabsorbent polymer film may have a thickness of 0.05 to 0.5 mm, a centrifugal retention capacity of 24 g/g to 48 g/g, and an elongation of 180% to 510%.

The superabsorbent polymer film may include a polymer in which an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group is neutralized is polymerized in the presence of a cellulose-based thickener and a humectant.

As described above, the superabsorbent polymer film of the present invention has excellent absorbency as well as flexibility and elasticity, waterproof and reinforcing materials such as diapers, wires and cables, electrolyte absorbers, flame retardants, wound protectors, freshness maintenance materials for food, soil repair materials, etc. can be used for a variety of purposes.

At the same time, the superabsorbent polymer film of the present invention exhibits expansion anisotropy, that is, when the superabsorbent polymer film is immersed in saline and swelled, the expansion rate in the thickness direction perpendicular to the plane is higher compared to the expansion rate in the plane direction. .

Specifically, the expansion anisotropy can be measured by the following method. A superabsorbent polymer film having an initial thickness of h is cut into a circle having a diameter d, and it is immersed in a 0.9 wt% sodium chloride aqueous solution at 25° C. for 60 minutes to free-swell. Thereafter, the swollen superabsorbent polymer film is removed from the aqueous sodium chloride solution, and moisture not absorbed into the superabsorbent polymer film is removed using a sieve. By measuring the diameter d' and the thickness h' of the swollen superabsorbent polymer film, the expansion anisotropy is calculated by dividing the expansion rate in the thickness direction (h'/h) by the expansion rate in the plane direction (d'/d).

[Equation 2]

The thicknesses (h, h') and diameters (d, d') are average values derived after each measurement at three or more different positions in the same superabsorbent polymer film using a microscope and a precision ruler.

The superabsorbent polymer film of the present invention is manufactured in the form of a thin film, unlike the existing superabsorbent polymer, and thus can be applied to the absorbent layer of a product by itself without additional processing or complexing with an auxiliary agent. Therefore, if the area of the superabsorbent polymer film expands excessively compared to the thickness when liquid is absorbed, there is a risk of deformation of the product, which is not preferable.

However, since the superabsorbent polymer film of the present invention has a high expansion anisotropy of 1.5 or more, it can exhibit excellent absorption performance while maintaining the shape of the product. Preferably, the expansion anisotropy of the superabsorbent polymer film may be 1.6 or more, 1.8 or more, 1.9 or more, 2.0 or more, or 2.3 or more, and 5 or less, or 4.5 or less, 4 or less, or 3.5 or less.

The shape of the superabsorbent polymer film is not particularly limited as long as the thickness thereof satisfies the above-mentioned range. That is, the superabsorbent polymer film may be in the form of a flat film having a constant thickness without irregularities on the surface, or may have a pattern formed on the surface to improve the flowability of the liquid. In this case, the shape of the pattern is not particularly limited, and the pattern may be formed by variously adjusting the length, width, depth, etc. of the concave and convex portions as necessary.

Meanwhile, according to another embodiment of the present invention, there is provided a method of manufacturing the super absorbent polymer film.

Specifically, the superabsorbent polymer film is

preparing a monomer composition by mixing an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized, a cellulose-based thickener, a moisturizing agent, a polymerization initiator, and a solvent;

casting the monomer composition on a substrate to form a film of the monomer composition;

forming a hydrogel polymer film by irradiating heat and/or light while stretching the monomer composition film; and

It may be prepared by a manufacturing method comprising the step of drying the hydrogel polymer film.

In the present invention, a film of a monomer composition is prepared from a solution of a monomer composition whose viscosity is controlled through a solution casting method, and the film is polymerized and dried to prepare a superabsorbent polymer in the form of a film.

In particular, in the present invention, by applying tension to the monomer composition film in the polymerization step and stretching it, the physical properties of the superabsorbent polymer film produced can be adjusted.

In the preparation method of the present invention, the monomer composition, which is a raw material for the super absorbent polymer, includes an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized, a cellulose-based thickener, a humectant, a polymerization initiator, and a solvent.

First, the acrylic acid-based monomer is a compound represented by the following formula (1):

[Formula 1]

R ¹ -COOM ¹

In Formula 1,

R ¹ is an alkyl group having 2 to 5 carbon atoms including an unsaturated bond,

M ¹ is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

Preferably, the acrylic acid-based monomer includes at least one selected from the group consisting of acrylic acid, methacrylic acid, and monovalent metal salts, divalent metal salts, ammonium salts and organic amine salts thereof.

Here, the acrylic acid-based monomer may have an acidic group and at least a portion of the acidic group is neutralized. Preferably, the monomer partially neutralized with an alkali material such as sodium hydroxide, potassium hydroxide, ammonium hydroxide and the like may be used. In this case, the degree of neutralization of the acrylic acid-based monomer may be 40 to 95 mol%, or 40 to 80 mol%, or 45 to 75 mol%. The range of the degree of neutralization may be adjusted according to the final physical properties. If the degree of neutralization is too high, it may be difficult for the polymerization to proceed smoothly due to precipitation of neutralized monomers.

In a preferred embodiment, as the alkali material, sodium hydroxide (NaOH), potassium hydroxide (KOH), or a combination thereof may be used. In particular, when potassium hydroxide is included, it is preferable to prepare a superabsorbent polymer film having better flexibility and dimensional stability.

The concentration of the acrylic acid-based monomer may be about 20 to about 60% by weight, preferably about 40 to about 50% by weight, based on the monomer composition including the raw material and solvent of the superabsorbent polymer, and the polymerization time and It may be an appropriate concentration in consideration of the reaction conditions and the like. However, if the concentration of the monomer is too low, the yield of the superabsorbent polymer may be low and there may be problems in economic feasibility. this may be lowered.

Meanwhile, in the present invention, a thickener and a moisturizing agent are included in the monomer composition so that the monomer composition can be applied in the form of a film through the solution casting method.

As a thickener and a humectant are included at the same time as described above, the monomer composition of the present invention exhibits a suitable viscosity for casting in a film form, can maintain an appropriate moisture content in the polymerization process after film casting, and the superabsorbent polymer film produced has high flexibility can represent

In the present invention, a cellulose-based thickener is used as the thickener, and specifically, it is selected from the group consisting of nanocellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and sodium carboxymethylcellulose. One or more of these may be used. Preferably, nanocellulose, hydroxyethylcellulose, sodium carboxymethylcellulose, or a combination thereof may be used.

The cellulose-based thickener is 0.01 parts by weight or more, 0.1 parts by weight or more, 0.2 parts by weight or more, or 0.4 parts by weight or more, and 5 parts by weight or less, 3 parts by weight or less, 1 part by weight or less based on 100 parts by weight of the solid content in the monomer composition. , or 0.9 parts by weight or less.

In this case, the solid content in the monomer composition means all components of the composition excluding the solvent. That is, the solid content means the total content of the acrylic acid-based monomer, an alkali material for neutralizing the acrylic monomer, a cellulose-based thickener, a moisturizing agent, a crosslinking agent, a thermal initiator, a photoinitiator, and an internal crosslinking agent.

If the content of the cellulosic thickener is less than 0.01 parts by weight based on 100 parts by weight of the solid content in the monomer composition, a sufficient thickening effect cannot be secured, so it may be difficult to prepare a film of the monomer composition. On the contrary, if it exceeds 5 parts by weight, the viscosity of the monomer composition is too high This increases the thickness of the film, and it may be difficult to uniformly control the film thickness.

The humectant may be used without limitation, a substance usually used as a moisturizing component in pharmaceuticals, cosmetics, chemical products, and the like. Examples of the moisturizer include at least one selected from the group consisting of polyhydric alcohols having two or more hydroxyl groups in the molecule, citric acid, and citrate.

Specifically, as the polyhydric alcohol, a polyhydric alcohol having 3 to 30 carbon atoms and containing 3 to 12 hydroxyl groups in a molecule may be used. In one example, the polyhydric alcohol is glycerin; diglycerin; ethylene glycol; propylene glycol; butylene glycol; sorbitol; polyethylene glycol; polyglycerin-3; polyglycerin-6; polyglycerin-10; and an ester compound of polyglycerol-10 and a saturated fatty acid having 3 to 18 carbon atoms (eg, polyglyceryl-10 distearate, polyglyceryl-10 oleate, polyglyceryl-10 laurate, etc.) It may be one or more selected from, among them, one or more selected from the group consisting of glycerin, diglycerin, propylene glycol, and sorbitol may be preferably used.

Citric acid and/or citric acid salts may also be used as moisturizers. Examples of the citric acid salt include triethylcitrate, methylcitrate, sodium citrate, trisodium 2-methylcitrate and the like.

The moisturizing agent is used in an amount of 5 parts by weight or more, 10 parts by weight or more, 20 parts by weight or more, or 30 parts by weight or more, and 70 parts by weight or less, 60 parts by weight or less, or 50 parts by weight or less based on 100 parts by weight of the acrylic acid-based monomer. It is preferable to be

If the content of the humectant is less than 5 parts by weight based on 100 parts by weight of the acrylic acid-based monomer, the moisture content of the film of the monomer composition is not sufficient, so that the film may dry out or crumble in the subsequent polymerization and drying process, and the flexibility of the superabsorbent polymer film produced There is a problem that cannot be secured. Conversely, if the content of the polyhydric alcohol exceeds 70 parts by weight based on 100 parts by weight of the acrylic acid-based monomer, there may be a problem in that the absorbency of the superabsorbent polymer film is reduced. Therefore, it is preferable that the content of the humectant satisfies the above range.

The monomer composition may optionally include an internal crosslinking agent for crosslinking the polymer. The internal crosslinking agent may be used in the manufacture of a conventional super absorbent polymer. More specifically, the internal crosslinking agent includes a crosslinking agent having at least one functional group capable of reacting with the water-soluble substituent of the acrylic acid monomer and at least one ethylenically unsaturated group; Alternatively, a crosslinking agent having two or more functional groups capable of reacting with a water-soluble substituent of the monomer and/or a water-soluble substituent formed by hydrolysis of the monomer may be used.

Specific examples of the internal crosslinking agent include bisacrylamide having 8 to 12 carbon atoms, bismethacrylamide, poly(meth)acrylate of a polyol having 2 to 10 carbon atoms, or poly(meth)allyl ether of a polyol having 2 to 10 carbon atoms. and the like, and more specifically, N,N'-methylenebis(meth)acrylate, ethyleneoxy(meth)acrylate, polyethyleneoxy(meth)acrylate, propyleneoxy(meth)acrylate, glycerin diacryl At least one selected from the group consisting of rate, glycerin triacrylate, trimethylol triacrylate, polyethylene glycol diacrylate, triallylamine, triaryl cyanurate, triallyl isocyanate, polyethylene glycol, diethylene glycol and propylene glycol can be used In one embodiment, polyethylene glycol diacrylate may be used as the internal crosslinking agent.

The internal crosslinking agent may be included in a concentration of 3000 ppm or less with respect to the monomer composition to crosslink the polymerized polymer. In one embodiment, the internal crosslinking agent may be included in an amount of 10 ppm or more, 50 ppm or more, 100 ppm or more, or 500 ppm or more, and 3000 ppm or less, 2500 ppm or less, 2000 ppm or less, 1500 ppm or less, or 1000 ppm or less. have.

The polymerization initiator used during polymerization in the method for preparing the superabsorbent polymer film of the present invention is not particularly limited as long as it is generally used in the manufacture of the superabsorbent polymer film.

Specifically, as the polymerization initiator, a thermal polymerization initiator or a photopolymerization initiator according to UV irradiation may be used according to a polymerization method. However, even by the photopolymerization method, a certain amount of heat is generated by irradiation such as ultraviolet irradiation, and a certain amount of heat is generated according to the progress of the polymerization reaction, which is an exothermic reaction, so a thermal polymerization initiator may be additionally included. According to a preferred embodiment, a photopolymerization initiator and a thermal polymerization initiator may be used simultaneously as the polymerization initiator.

The photopolymerization initiator may be used without limitation as long as it is a compound capable of forming radicals by light such as ultraviolet rays.

As the photopolymerization initiator, for example, benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, benzyl dimethyl ketal Ketal), acyl phosphine (acyl phosphine) and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. On the other hand, as a specific example of the acylphosphine, commercially available lucirin TPO (2,4,6-Trimethylbenzoyldiphenylphosphine oxide), Irgacure 819 (Phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide), and the like can be mentioned. For a wider variety of photoinitiators, see Reinhold Schwalm, "UV Coatings: Basics, Recent Developments and New Applications (Elsevier 2007)," p. 115, and not limited to the above example.

The photopolymerization initiator may be included in an amount of 10 ppm or more, 20 ppm or more, or 40 ppm or more, and 2000 ppm or less, 1000 ppm or less, 500 ppm or less, or 100 ppm or less with respect to the monomer composition. If the concentration of the photopolymerization initiator is too low, the polymerization rate may be slowed, and if the concentration of the photopolymerization initiator is too high, the molecular weight of the superabsorbent polymer may be small and physical properties may be non-uniform.

In addition, as the thermal polymerization initiator, at least one selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of the persulfate-based initiator include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), ammonium persulfate (Ammonium persulfate; (NH ₄ ) ₂ S ₂ O ₈ ) and the like, and examples of the azo-based initiator include 2,2-azobis-(2-amidinopropane) dihydrochloride (2,2-azobis(2-amidinopropane) dihydrochloride), 2 ,2-Azobis-(N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoylazo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane]dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride) and 4,4-azobis-(4-cyanovaleric acid) (4,4-azobis-(4-cyanovaleric acid)). For more various thermal polymerization initiators, see Odian's book 'Principle of Polymerization (Wiley, 1981)', p. 203, and not limited to the above example.

The thermal polymerization initiator may be included in the monomer composition in an amount of 10 ppm or more, 100 ppm or more, or 500 ppm or more, and 2000 ppm or less, 1500 ppm or less, or 1000 ppm or less. When the concentration of the thermal polymerization initiator is too low, additional thermal polymerization hardly occurs and the effect of adding the thermal polymerization initiator may be insignificant. have.

In the manufacturing method of the present invention, the monomer composition may further include additives such as a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

Raw materials such as the above-described acrylic acid-based unsaturated monomer, internal crosslinking agent, polymerization initiator, and additive are prepared in the form of a monomer composition solution dissolved in a solvent.

The solvent that can be used can be used without limitation in its composition as long as it can dissolve the above-mentioned components, for example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene glycol. , Ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl ether , toluene, xylene, butyrolactone, carbitol, methyl cellosolve acetate, and N,N-dimethylacetamide may be used in combination. For example, water may be used as the solvent.

In the present invention, the monomer composition exhibits a viscosity suitable for the solution casting method, including a cellulose-based thickener and a moisturizing agent. Specifically, the viscosity at 25 ° C. of the monomer composition is 100 mPa · s or more, 150 mPa · s or more, 200 mPa · s or more, or 240 mPa · s or more, and 5000 mPa · s or less, 2300 mPa · s or less, 2000 mPa·s or less, or 1600 mPa·s or less. The viscosity of the monomer composition may be measured with a viscometer (eg, TV-22 manufactured by TOKI Corporation) under the conditions of spindle #1 and a rotational speed of 1 rpm.

If the viscosity of the monomer composition is less than 100 mPa·s, it may be difficult to cast the monomer composition to a uniform thickness and polymerize while stretching the monomer composition. Conversely, when the viscosity of the monomer composition exceeds 5000 mPa·s, it is difficult to prepare a uniform monomer composition, and the flowability of the monomer composition is low, which is not preferable because processability is deteriorated, and defoaming is difficult.

After preparing the monomer composition, it is cast on a substrate to prepare a film of the monomer composition, stretched and simultaneously polymerized to form a hydrogel polymer film. Casting and polymerization of the monomer composition may be continuously performed through a roll-to-roll process.

First, a monomer composition is applied on a substrate to prepare a film of the monomer composition.

The material of the substrate is not particularly limited, but it is preferable to use a material in which the monomer composition is easily applied and the hydrogel polymer film is easily separated after polymerization.

Specifically, as the substrate, a polyethylene terephthalate (PET) film having at least one surface hydrophobically treated with silicone or fluorine, which is usually used as a release film, may be used. For example, the substrate may be a PET film surface-treated with a siloxane-based polymer or polytetrafluoroethylene (Teflon ^{® ).} However, the material of the substrate is not limited thereto, and a suitable substrate may be selected according to the composition and properties of the monomer composition.

In general, in the polymer solution casting method, the solvent is removed after casting the polymer solution, in the present invention, after the monomer composition is applied on the substrate, stretching and polymerization are performed immediately so as not to decrease the moisture content.

If the moisture content of the film of the monomer composition is too low, components constituting the monomer composition before polymerization may be precipitated, and there may be a problem in that the film is broken after polymerization. Accordingly, the moisture content of the monomer composition film preferably satisfies the range of 30 wt% to 60 wt%, and preferably satisfies the range of 30 wt% to 50 wt%, or 30 wt% to 45 wt%.

The thickness of the monomer composition film may be appropriately adjusted according to the desired thickness of the superabsorbent polymer film. Although the thickness of the monomer composition film hardly changes during the polymerization step, the thickness may decrease by about 10 to 40%, or 15 to 35%, while the moisture content decreases during the drying process of the hydrogel polymer film after polymerization. A film of the monomer composition is prepared to an appropriate thickness.

As an example, the thickness of the film of the monomer composition is 0.8 mm or less, 0.6 mm or less, or 0.5 mm or less, and may be 0.001 mm or more, or 0.01 mm or more, but is not limited thereto, and the composition of the monomer composition, polymerization, and drying step It can be appropriately adjusted according to the specific conditions of the superabsorbent polymer film thickness and the desired thickness.

Next, a polymerization reaction is performed by irradiating heat and/or light while stretching the monomer composition film in the longitudinal direction (MD direction) to form a hydrogel polymer film. By stretching the film during polymerization as described above, physical properties such as elongation and expansion anisotropy can be controlled.

At this time, the tension applied to the monomer composition film is 40 N/m or more, or 45 N/m or more, or 50 N/m or more, or 60 N/m or more and 100 N/m or less, or 90 N/m or less, or It may be 80 N/m or less. If the film is stretched by applying an excessively large tension, there may be a problem in that the film of the monomer composition is broken or the thickness is excessively thin.

The polymerization temperature may be appropriately adjusted depending on the composition of the monomer composition, but is preferably 40° C. or 50° C. or higher for smooth reaction progress. In addition, when the temperature is too high, the solvent evaporates and components constituting the monomer composition may be precipitated. Therefore, the polymerization temperature is preferably 90°C or less or 80°C or less.

The water content of the hydrogel polymer film prepared through the polymerization step may be about 20 wt% or more, preferably 25 wt% or more, and 40 wt% or less, or 35 wt% or less. Accordingly, the water-containing gel polymer film is dried so that the water content is 15% by weight or less to prepare a final superabsorbent polymer film.

The temperature of the drying step may be preferably in the range of 80 to 150 ℃, or 90 to 100 ℃. By drying for about 5 to 30 minutes within the above temperature range, the moisture content is 15% by weight or less, or 12% by weight or less, or 10% by weight or less. Alternatively, it is possible to obtain a superabsorbent polymer film of 9 wt% or less and 1 wt% or more, or 2 wt% or more, or 4 wt% or more, or 6 wt% or more.

As described above, the superabsorbent polymer film prepared according to the manufacturing method satisfies a thickness of 0.5 mm or less and an expansion anisotropy of 1.5 or more, and exhibits excellent absorption and mechanical properties. Since the superabsorbent polymer film of the present invention can be used as an absorber by itself without the need for complexing with an auxiliary agent such as pulp, it can be suitably used for slim and thin-film products, and can exhibit excellent absorption performance without deformation of the product.

Hereinafter, preferred examples are presented to help the understanding of the present invention, but the following examples are merely illustrative of the present invention, and it will be apparent to those skilled in the art that various changes and modifications are possible within the scope and spirit of the present invention, It goes without saying that changes and modifications fall within the scope of the appended claims.

[Example]

Example 1

A neutralized solution in which 70 mol% of acrylic acid was neutralized was prepared by mixing 55 g of acrylic acid, 66.6 g of a 45 wt% solution of potassium hydroxide (KOH), and 55 g of water.

Hydroxyethyl cellulose (HEC, Natrosol 250HR from Ashland) as a thickener, glycerin as a plasticizer, sodium persulfate as a thermal polymerization initiator, and Irgacure 819 as a photoinitiator were added to the neutralizing solution to prepare a monomer composition having a solid content of 54 wt% did.

At this time, HEC was added in an amount of 0.45 parts by weight based on 100 parts by weight of the solid content of the monomer composition, glycerin was added in an amount of 40 parts by weight based on 100 parts by weight of acrylic acid, the thermal polymerization initiator was added in an amount of 1000 ppm based on the total weight of the monomer composition, and 80 ppm of the photopolymerization initiator was added. .

The viscosity at 25° C. of the prepared monomer composition was measured with a TV-22 equipment manufactured by TOKI, 1 rpm, and Rotor #1, and as a result, the viscosity of the monomer composition was confirmed to be 247 mPa·s.

Next, the monomer composition was coated on one surface of a polyethylene terephthalate (PET) release film (Mitsubishi MRL film) whose surface was hydrophobically treated with a siloxane-based polymer to form a 0.1 mm thick monomer composition film (moisture content of 30%). A comma coater (Gap 365 μm) was used for the coating, and the moving speed of the applicator roll was 0.5 m/min.

Then, polymerization was carried out by irradiating ultraviolet rays of 370 mJ/cm ^{2 to the monomer composition film to form a hydrogel polymer film.} At this time, the polymerization reaction was carried out while stretching the monomer composition film at a tension of 60 N/m in the MD direction. The thickness of the prepared hydrogel polymer film was 0.1 mm, and it was confirmed that there was no significant change compared to the monomer composition, and the moisture content was 30% by weight.

Next, the prepared hydrogel polymer film was dried at a temperature of 90° C. for 10 minutes to prepare a superabsorbent polymer film (SAP film) having a moisture content of 9.84 wt% and a thickness of 0.083 mm.

Examples 2 to 4

Polyethylene glycol diacrylate (PEGDA, MW=400, manufacturer: Aldrich) is further included in the monomer composition as an internal crosslinking agent, and the composition of the monomer composition and the thickness of the film of the monomer composition are as shown in Table 1 below, Superabsorbent polymer films of Examples 2 to 4 were prepared in the same manner as in Example 1.

Example 5

Instead of HEC as a thickener, sodium carboxymethyl cellulose (CMC, average weight average molecular weight 250,000, degree of substitution 0.7) was used at 0.68 parts by weight based on 100 parts by weight of solids in the monomer composition, and 2000 ppm of PEGDA as an internal crosslinking agent (relative to the total weight of the monomer composition) A monomer composition was prepared in the same manner as in Example 1, except that it was further included.

The monomer composition was coated on one side of a polyethylene terephthalate (PET) release film whose surface was hydrophobically treated with a siloxane-based polymer to a thickness of 0.2 mm to form a monomer composition film, and UV light ^{of 370 mJ/cm 2 was applied to the monomer composition film.} It was irradiated and polymerized to form a hydrogel polymer film. At this time, the monomer composition film was stretched by applying a tension of 60 N/m in the MD direction to proceed with polymerization.

Next, the prepared hydrogel polymer film was dried at a temperature of 110° C. for 15 minutes to prepare a super absorbent polymer film.

Example 6

A monomer composition was prepared in the same manner as in Example 1, except that propylene glycol was used instead of glycerin as a moisturizer, and 2000 ppm of PEGDA (relative to the total weight of the monomer composition) was further included as an internal crosslinking agent.

The monomer composition was coated on one side of a polyethylene terephthalate (PET) release film whose surface was hydrophobically treated with a siloxane-based polymer to a thickness of 0.2 mm to form a monomer composition film, and UV light ^{of 370 mJ/cm 2 was applied to the monomer composition film.} It was irradiated and polymerized to form a hydrogel polymer film. At this time, the monomer composition film was stretched by applying a tension of 60 N/m in the MD direction to proceed with polymerization.

Next, the prepared hydrogel polymer film was dried at a temperature of 110° C. for 15 minutes to prepare a super absorbent polymer film.

Example 7

A superabsorbent polymer film was prepared in the same manner as in Example 3, except that the stretching tension applied to the monomer composition film during polymerization was 80 N/m.

Comparative Example 1

Referring to Example 1 of Japanese Patent Application No. 1995-154195 (Japanese Patent Application Laid-Open No. Hei 08-73507), a sheet-type super absorbent polymer was prepared by the following method.

36 g of acrylic acid, 37.3 g of triethanolamine, 0.08 g of trimethylolpropane triacrylate, 18.3 g of deionized water, 0.1 g of potassium persulfate, 0.0025 g of L-ascorbic acid (oxidation/reduction initiator), and 0.92 g of hydroxyethyl cellulose A monomer composition comprised (about 75 weight% of acrylic acid triethanolamine salt, about 25 weight% of acrylic acid, and about 80 weight% of monomer concentration in a monomer composition among all monomers) was prepared. This monomer composition was sandwiched between two Teflon sheets and heated and polymerized in a hot air dryer at 80°C under the conditions of a clearance of 0.5 mm to obtain a sheet-like superabsorbent polymer having a thickness of 0.434 mm. The water content of the prepared superabsorbent polymer was found to be 6.62 wt%, and a separate drying process was not performed after polymerization.

Comparative Example 2

Referring to Example 3 of Japanese Patent Application No. 1995-154195 (Japanese Patent Application Laid-Open No. Hei 08-73507), a sheet-type super absorbent polymer was prepared by the following method.

Acrylic acid 36g, triethanolamine 14.9g, potassium hydroxide (KOH) 8.4g, trimethylolpropane triacrylate 0.05g, deionized water 14.8g, potassium persulfate 0.1g, and L-ascorbic acid 0.0025g, hydroxyethylcellulose 0.7 A monomer composition composed of g was prepared. This monomer composition was sandwiched between two Teflon sheets and subjected to heat polymerization in a hot air dryer at 80° C. under the conditions of a clearance of 1 mm to obtain a sheet-like superabsorbent polymer having a thickness of 1.063 mm. The water content of the prepared superabsorbent polymer was confirmed to be 10.4 wt%, and a separate drying process was not performed after polymerization.

Comparative Example 3

A neutralized solution in which 70 mol% of acrylic acid was neutralized was prepared by mixing 55 g of acrylic acid, 66.6 g of a 45 wt% solution of potassium hydroxide (KOH), and 55 g of water.

Hydroxyethyl cellulose (HEC, 250HR from Ashland), glycerin, and sodium persulfate as a thermal polymerization initiator were added to the neutralization solution to prepare a monomer composition having a solid content of 54 wt%.

At this time, HEC was added in an amount of 0.45 parts by weight based on 100 parts by weight of the solid content of the monomer composition, glycerin was added in an amount of 40 parts by weight based on 100 parts by weight of acrylic acid, and sodium persulfate as a thermal polymerization initiator was added at 1000 ppm based on the total weight of the monomer composition.

This monomer composition was sandwiched between two Teflon sheets and subjected to heat polymerization in a hot air dryer at 80° C. under a clearance of 1 mm to obtain a sheet-like hydrogel polymer having a thickness of 1 mm and a moisture content of 10% by weight.

Next, the prepared hydrogel polymer was dried at a temperature of 110° C. for 10 minutes to prepare a sheet-type superabsorbent polymer having a moisture content of 9.5% by weight and a thickness of 0.976 mm.

Comparative Example 4

A sheet-type superabsorbent polymer was prepared in the same manner using the same monomer composition as in Comparative Example 1, but by controlling the clearance, a sheet-type superabsorbent polymer having a thickness of 0.357 mm and a moisture content of 8.91 wt% was prepared.

Comparative Example 5

A sheet-type super absorbent polymer was prepared in the same manner as in Example 2, except that glycerin was not included during the preparation of the monomer composition and the thickness of the film of the monomer composition was set to 0.1 mm.

Comparative Example 6

A superabsorbent polymer film was prepared in the same manner as in Example 3, except that the monomer composition film was not stretched during polymerization.

Comparative Example 7

Referring to Example 14 of Japanese Patent Application Laid-Open No. Hei 09-183856, a sheet-type super absorbent polymer was prepared by the following method.

In a 1L beaker, 400 ml of cyclohexane and 1.6 g of HLB 6 sucrose fatty acid ester surfactant were added and stirred to prepare a reaction solvent for reverse-phase suspension polymerization.

To 110.7 g of a 35% aqueous monomer solution with a solid content of acrylic acid and sodium acrylate (75% neutralization degree) as a monomer component, 5.85 mg of N,N-methylenebisacrylamide as an internal crosslinking agent, and 193.6 mg of hydroxyethylcellulose (HEC) as a thickener It was dissolved to prepare an aqueous monomer solution. Then, 58.5 mg of potassium persulfate, a polymerization initiator, was added and dissolved while bubbling nitrogen gas in the aqueous monomer solution.

An aqueous monomer solution in which a polymerization initiator was dissolved was added to the prepared reverse-phase suspension polymerization solvent, followed by stirring at 60° C. for 2 hours to proceed with polymerization to obtain a gel-like polymer.

After drying the obtained polymer at 160° C., 2 g of glycerin was added to 8 g of the dried polymer particles, and water was sprayed so that the moisture content was 20%. The polymer particles to which glycerin and water have been added are uniformly spread on a 10 cm * 10 cm plate, and left in a constant temperature and humidity room (25° C., RH 90%) for 10 minutes, followed by a temperature of 150° C. and a pressure of 350 gf/cm ² A sheet-type superabsorbent polymer having a thickness of 1.042 mm was prepared by rolling with a furnace for 5 minutes.

	Monomer composition film thickness (mm)	Monomer composition viscosity (mPas) 1)	Monomer neutralization degree (%)	Content in the monomer composition
				Solid content (%)	thickener (parts by weight)	Internal crosslinking agent (ppm)	Thermal initiator (ppm)	Photoinitiator (ppm)	Oxidation/reduction initiator (ppm)
Example 1	0.1	247	70	54	0.45	0	1000	80	0
Example 2	0.15	247	70	54	0.45	500	1000	80	0
Example 3	0.1	201	70	54	0.45	1000	1000	80	0
Example 4	0.4	1383	70	54	0.75	500	1000	80	0
Example 5	0.2	332	70	54	0.68	2000	1000	80	0
Example 6	0.2	562	70	54	0.45	2000	1000	80	0
Example 7	0.1	215	70	54	0.45	1000	1000	80	0
Comparative Example 1	-	n/a	75	80.3	0.99	863	1079	0	27
Comparative Example 2	-	n/a	68	80.3	0.93	667	1334	0	33
Comparative Example 3	One	1189	70	54	0.75	2000	1000	0	0
Comparative Example 4	-	n/a	75	80.3	0.99	863	1079	0	27
Comparative Example 5	0.1	245	70	54	0.45	500	1000	80	0
Comparative Example 6	0.1	215	70	54	0.45	1000	1000	80	0
Comparative Example 7	-	n/a	75	40	0.17	200	2000	0	0

In Table 1, the content of each component except for the thickener in the monomer composition was expressed in weight % or ppm based on the total weight of the monomer composition, and the content of the thickener was expressed in parts by weight based on 100 parts by weight of the solid content of the monomer composition.

Since the monomer compositions of Comparative Examples 1, 2, and 4 contained an oxidation/reduction initiator, polymerization was initiated during the measurement, which made it impossible to measure the viscosity of the monomer composition. In Comparative Example 7, since the reversed-phase suspension polymerization method was used, the viscosity of the monomer composition was not separately measured.

Experimental example

The physical properties of the superabsorbent polymer film or sheet of each Example and Comparative Example were evaluated by the following method, and the results are summarized in Tables 2 and 3 below.

(1) moisture content

The moisture content was calculated from the weight before drying (a) and the weight after drying (b) of the superabsorbent polymer film (or sheet) specimen. At this time, the drying of the specimen was performed in such a way that the temperature was increased from room temperature (25° C.) to 150° C. over 5 minutes, and then maintained at 150° C. for 15 minutes.

Moisture content (%) = (a-b)/a*100

(2) Thickness of superabsorbent polymer film (or sheet)

Using a film thickness gauge manufactured by Mitutoyo, the thickness was measured at three different positions in the superabsorbent polymer film (or sheet), and the average value thereof was calculated.

(3) Centrifugation retention capacity (CRC, g/g)

Centrifugation retention capacity (CRC) was measured according to the method of EDANA method WSP 241.2. The moisture content of the superabsorbent polymer of each Example and Comparative Example to be measured is as shown in Table 2 below, and the centrifugation retention capacity was measured without a separate moisture content adjustment.

Specifically, the superabsorbent polymer film or sheet is cut to have a weight (W0) of 0.08 to 0.12 g, placed in a non-woven bag, and sealed, and then immersed in 0.9 wt% sodium chloride aqueous solution (physiologic saline) at room temperature. did it After 30 minutes, the bag was drained of water for 3 minutes under the condition of 250G using a centrifuge, and the mass W2 (g) of the bag was measured. Moreover, after performing the same operation without using resin, the mass W1 (g) at that time was measured. Using each obtained mass, CRC (g/g) was calculated according to the following formula.

CRC (g/g) = {[W2(g) - W1(g)]/W0(g)} - 1

(4) elongation (%)

Prepare a specimen by cutting a superabsorbent polymer film or sheet into a rectangular shape with a size of 20 mm x 60 mm so that the cut surface is smooth. The following specimens were mounted. The specimen was tensioned at a rate of 0.5 mm per minute to measure the gage distance at the time when the specimen fracture occurred, and the elongation was obtained by dividing the value by the initial gage distance.

[Equation 1]

Elongation (%) = (L _1- L ₀ )/L ₀ *100

In Equation 1 above,

L ₀ is the initial gage distance,

L ₁ is the gage point distance at the time of fracture.

(5) expansion anisotropy

A superabsorbent polymer film (or sheet, hereinafter the same) having an initial thickness of h was cut into a circle having a diameter d, and it was immersed in a 0.9 wt% sodium chloride aqueous solution at 25° C. for 60 minutes to free-swell. Thereafter, the swollen superabsorbent polymer film was removed from the aqueous sodium chloride solution, and moisture not absorbed into the superabsorbent polymer film was removed using a sieve. By measuring the diameter d' and thickness h' of the swollen superabsorbent polymer film, the expansion anisotropy was calculated by dividing the thickness direction expansion rate (h′/h) by the in-plane expansion rate (d′/d).

[Equation 2]

In this case, the thicknesses (h, h') and diameters (d, d') are average values derived after measurement at three or more different positions in the same superabsorbent polymer film using a microscope and a precision ruler.

In this experimental example, the initial diameter (d) of the superabsorbent polymer film specimen was 15 mm, and the h, h', and d' values of each specimen are shown in Table 2 below.

(6) Total light transmittance (%) and yellowness (Yellow Index)

Total light transmittance for visible light and yellowness according to ASTM D1925 standard were measured using COH-400 (NIPPON DENSHOCU) equipment.

(7) Flexural test (flexibility)

The flexibility of each superabsorbent polymer film or sheet was checked according to ASTM D522 using a Cylindrical Mandrel Bend Tester (KP M5500). For the test, a mandrel having a diameter of 4 mm (4R) was used, and it was judged as X if it was broken or cracked, and O if it maintained its shape.

	Moisture content (%)	CRC (g/g)	Elongation (%)	electric light Transmittance (%)	yellowness	flexibility
Example 1	9.84	46.3	227.8	91.78	1.29	O
Example 2	9.65	37.4	252.1	92.12	1.11	O
Example 3	9.88	28	187.9	92.12	1.01	O
Example 4	9.92	30.2	506.4	90.46	2.30	O
Example 5	11.3	26.4	124.2	91.90	0.49	O
Example 6	11.7	23.1	102.9	90.60	0.72	O
Example 7	9.89	24.5	184.5	92.32	1.01	O
Comparative Example 1	6.62	22.7	526.0	89.24	1.91	O
Comparative Example 2	10.4	7.2	379.0	89.32	3.41	O
Comparative Example 3	9.50	8.7	515.4	90.98	1.42	O
Comparative Example 4	8.91	13.5	568.8	89.39	3.17	O
Comparative Example 5	9.22	21.1	11.5	91.87	0.87	X
Comparative Example 6	9.29	20.8	98	90.05	1.27	O
Comparative Example 7	10.5	5.1	173.6	0	45.2	X

	h (mm)	h' (mm)	d' (mm)	expansion anisotropy
Example 1	0.083	0.833	46	3.3
Example 2	0.114	0.915	48	2.5
Example 3	0.072	0.453	41	2.3
Example 4	0.260	1.488	47	1.8
Example 5	0.192	1.066	49	1.7
Example 6	0.194	1.028	53	1.5
Example 7	0.086	0.423	39	1.9
Comparative Example 1	0.434	1.387	49	1.0
Comparative Example 2	1.063	2.786	34	1.2
Comparative Example 3	0.976	3.645	38	1.5
Comparative Example 4	0.357	1.427	46	1.3
Comparative Example 5	0.054	0.134	42	0.9
Comparative Example 6	0.094	0.652	50	2.1
Comparative Example 7	1.083	1.246	20	0.86

The superabsorbent polymer film prepared according to the above example was in the form of a film having high transparency and flexibility, and showed a different shape from the existing superabsorbent polymer sheet. In addition, referring to Tables 2 and 3, it can be seen that the superabsorbent polymer film of Examples has a thinner thickness and excellent absorbency compared to the conventional superabsorbent polymer sheet, and at the same time exhibits high elongation and expansion anisotropy.

Claims (12)

1. A superabsorbent polymer film comprising a polymer having an acidic group and polymerized with an acrylic acid-based monomer in which at least a portion of the acidic group is neutralized, the superabsorbent polymer film comprising:

   having a thickness of 0.001 to 0.5 mm,

   a centrifugal retention capacity (CRC) of 23 g/g or more, measured according to EDANA method WSP 241.2;

   A superabsorbent polymer film having an elongation of 100% or more calculated by the following Equation 1:

   [Equation 1]

   Elongation (%) = (L _1- L ₀ )/L ₀ *100

   In Equation 1 above,

   L ₀ is the initial gage distance,

   L ₁ is the gage point distance at the time of fracture when the specimen is pulled at a rate of 0.5 mm per minute.
2. According to claim 1,

   A superabsorbent polymer film having a centrifugation retention capacity of 23 g/g to 50 g/g and an elongation of 100% to 550%.
3. According to claim 1,

   When the circularly cut superabsorbent polymer film was immersed in 0.9 wt% sodium chloride aqueous solution to swell for 60 minutes, and then the thickness and diameter were measured, the superabsorbent polymer film having an anisotropy of expansion of 1.5 or more as expressed by Equation 2 below:

   [Equation 2]

   

   In Equation 2 above,

   h is the initial thickness of the superabsorbent polymer film, h' is the thickness after swelling,

   d is the initial diameter of the superabsorbent polymer film, and d' is the diameter after swelling.
4. 4. The method of claim 3,

   A superabsorbent polymer film having an expansion anisotropy of 1.5 to 5.
5. According to claim 1,

   A superabsorbent polymer film having a total light transmittance of 89.5% or more.
6. preparing a monomer composition by mixing an acrylic acid-based monomer having an acidic group and at least a portion of the acidic group neutralized, a cellulose-based thickener, a moisturizing agent, a polymerization initiator, and a solvent;

   casting the monomer composition on a substrate to form a film of the monomer composition;

   forming a hydrogel polymer film by irradiating heat and/or light while stretching the monomer composition film; and

   The method for producing the superabsorbent polymer film of claim 1, comprising drying the hydrogel polymer film.
7. 7. The method of claim 6,

   The cellulose-based thickener is at least one selected from the group consisting of nanocellulose, hydroxyethylcellulose, hydroxypropylcellulose, hydroxyethylmethylcellulose, hydroxypropylmethylcellulose, and sodium carboxymethylcellulose. Way.
8. 7. The method of claim 6,

   The moisturizer is glycerin; diglycerin; ethylene glycol; propylene glycol; butylene glycol; sorbitol; polyethylene glycol; polyglycerin-3; polyglycerin-6; polyglycerin-10; an ester compound of polyglycerol-10 and a saturated fatty acid having 3 to 18 carbon atoms; citric acid; triethyl citrate; methyl citrate; sodium citrate; and trisodium 2-methylcitrate.
9. 7. The method of claim 6,

   The method for producing a superabsorbent polymer film, wherein the cellulose-based thickener is included in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the solid content in the monomer composition.
10. 7. The method of claim 6,

    The method for producing a superabsorbent polymer film, wherein the moisturizing agent is included in an amount of 5 to 70 parts by weight based on 100 parts by weight of the acrylic acid-based monomer.
11. 7. The method of claim 6,

    A method for producing a superabsorbent polymer film wherein the monomer composition has a viscosity at 25° C. of 100 mPa·s or more.
12. 7. The method of claim 6,

    In the step of forming the hydrogel polymer film, the tension applied to the monomer composition film is 40 to 100 N/m.